Things that can be explored in the region - best with 'external' accommodation for one or more days.
Venice, Padua, Verona, Bologna and Florence are famous (and touristy) places. Require at least one night away. Venice may be reached in 2.5-3 hours with parking across the dam and sailing with the Vaporetto to St. Marcs Square. Have a nice dinner at the Grand Canal and get back to bed before midnight! Florence may be reached in ≈ 4-5 hours.
Slovenia: Triglav National Park has beautiful mountains and lakes. The charming capital, Ljubljana, can be reached in 2 hours. The Soča river is unique with its magic color. Lots of activities on the river and lakes, especially in the Summer.
Croatia: Plitviçe National Park. This park Southeast of Zagreb is utterly unique, click here.